Meta-analysis of the net ecosystem carbon budget of European grasslands

The agricultural sector's role in climate change is a topic of debate and uncertainty, particularly regarding the soil carbon sequestration effect of grasslands. Numerous studies have examined specific grassland sites using the net ecosystem carbon budget (NECB) approach based on the eddy-covariance (EC) method for measuring the CO₂ exchange with the atmosphere and the quantification of ‘lateral’ carbon exports and imports (e.g., harvest and organic fertilizer application). Finding clear and consistent numbers is often complicated by issues of nomenclature and methodology of the carbon budget calculations and presentation in the literature or by missing information about management and lateral carbon flux details.

This review aims to synthesize current data on the NECB of European grasslands (excluding organic soils). For this purpose, a detailed search and screening of the currently available peer-reviewed literature regarding EC-based NECB of grasslands in Europe was conducted. Data for 43 different sites in 16 countries passed the screening and quality checks, totaling 147 site-years of NECB measurements. The gathered NECB data for grasslands are scattered over a large range of NECB values between about –350 and +350 g C m⁻² yr⁻¹. The overall average of −33 g C m⁻² yr⁻¹ indicates a slight carbon sink, although with a large uncertainty. We could not detect a significant spatial distribution pattern of source or sink sites. In addition, we found that sites at the same location can act as sources or sinks depending on the management practice of the fields. For an improved assessment, a more consistent and complete data reporting of all flux measurement sites would be useful.